ANATOMY AND PHYSIOLOGY 



and here also there was much obscurity about the ex- 

 act method of functioning at the time of the revival of 

 physiological chemistry. That oxygen is consumed 

 and carbonic acid given off during respiration the 

 chemists of the age of Priestley and Lavoisier had in- 

 deed made clear, but the mistaken notion prevailed 

 that it was in the lungs themselves that the important 

 burning of fuel occurs, of which carbonic acid is a 

 chief product. But now that attention had been called 

 to the importance of the ultimate cell, this miscon- 

 ception could not long hold its ground, and as early as 

 1842 Liebig, in the course of his studies of animal heat, 

 became convinced that it is not in the lungs, but in the 

 ultimate tissues to which they are tributary, that the 

 true consumption of fuel takes place. Reviving La- 

 voisier's idea, with modifications and additions, Liebig 

 contended, and in the face of opposition finally de- 

 monstrated, that the source of animal heat is really 

 the consumption of the fuel taken in through the 

 stomach and the lungs. He showed that all the activ- 

 ities of life are really the product of energy liberated 

 solely through destructive processes, amounting, broad- 

 ly speaking, to combustion occurring in the ultimate 

 cells of the organism. Here is his argument: 



LIEBIG ON ANIMAL HEAT 



"The oxygen taken into the system is taken out 

 again in the same forms, whether in summer or in 

 winter ; hence we expire more carbon in cold weather, 

 and when the barometer is high, than we do in warm 

 weather; and we must consume more or less carbon 

 in our food in the same proportion; in Sweden more 



